The AIMD Additive Increase Multiplicative Decrease CA algorithm halves the size of the congestion window when a loss has been detected. But what experimental/statistical or theoretical evidence is there to suggest that dividing by 2 is the most efficient method (instead of, say, another numerical value), other than "intuition"? Can someone point me to a publication or journal paper that supports this or investigates this claim?
All of the algorithms here
https://en.wikipedia.org/wiki/TCP_congestion_control#Algorithms
alter the congestion window in one form or another and they all have varying results which is to be expected.
Can someone point me to a publication or journal paper that supports this or investigates this claim?
Yang Richard Yang & Simon S. LamThere's paper investigates it in this paper
http://www.cs.utexas.edu/users/lam/Vita/Misc/YangLam00tr.pdf
We refer to this window adjustment strategy as general additive increase multiplicative decrease (GAIMD). We present the (mean) sending rate of a GAIMD flow as a function of α, β.
The authors parameterized the additive and multiplicative parts of AIMD and then studied them to see if they could be improved on for various TCP flows. The paper goes into a fair amount of depth on what they did and what the effects were. To summarize...
We found that the GAIMD flows were highly TCP-friendly. Furthermore, with β at 7/8 instead of 1/2, these GAIMD flows have reduced rate fluctuations compared to TCP flows.
If we believe the papers conclusion then there is no reason to believe that 2 is a magic bullet. Personally I doubt there is a best factor because it's based on too many variable ie protocol, types of flow etc.